1. Field of the Invention
This invention relates to a film circuit substrate exposure apparatus mainly used for the manufacture of flexible printed circuits.
2. Description of the Prior Art
A flexible printed circuit(hereinafter referred to as FPC) which is used for the assembly of film carrier type semiconductor devices, liquid crystal boards, cameras and table calculators usually consists of a polyester film or polyimide film having a thickness of 25 to 125 microns as substrate material.
Such film for FPC, which photoresist is coated on, is exposed to light by an exposure apparatus and then etched for mounting of IC and other circuit elements by means of bonding. Therefore, although the FPC is a "printed" circuit, it requires as high accuracy as comparable to that for "Integrated Circuit".
FIG. 3 is a view for explaining a prior art exposure apparatus and method of use of the same apparatus. Referring to the Figure, reference numeral 1 designates exposure light source including a short arc discharge lamp and a mirror, 2 illumination lens system including an integrator lens, and 3 reticle, which is supported on reticle support 5 movable in a horizontal plane in two directions X and Y by x-y driver 4 and 6 circumferential reticle driver. These drivers are mounted together with reticle support 5 on image projection cylinder 7. Image projection cylinder 7 is secured to stand 25 via holder 9. Reference numeral 8 designates screw member for moving image projection cylinder 7 in vertical direction Z. Screw member 8 has a female thread corresponding to a male thread formed in cylinder 7. Reference numeral 16 designates projection lens supported in projection lens holder 12. Reference numeral 15 designates screw member for moving projection lens holder 12 in vertical direction Z. Member 15 has a female thread corresponding to a male thread formed in cylinder 7. Reference numerals 10 and 11 designate engagement mechanisms consisting of keys and key grooves for restricting cylinder 7 and holder 12 to movement in vertical direction Z. Reference numeral 13 designates illumination lens system holder.
Reference numeral 17 designates FPC film with perforations 17'. Film 17 is fed to predetermined extent by a pair of predetermined extent feed rollers 18. Reference numeral 19 designates film receiver, which put down film 17 when it is pressed up by pressing member 21 with positioning pins 20. Film receiver 19 has pin escapement grooves 19' for pins 20. Film pressing member 21 has two rows of pins, only one of which is shown. Reference numeral 14 designates linear driver for driving film pressing member 21, 22 driver guide member, and 23 drive section.
With this exposure apparatus, a pattern of reticle 3 is projected onto FPC film 17. To this end, the position of the reticle is adjusted with X-Y driver 4 and circumferential reticle driver 6 such as to permit projection with reference to perforations of film 17. In addition, for providing normal focusing and magnification projection cylinder 7 and projection lens holder 12 are adjusted by turning screw members 8 and 15. In this adjustment, members 7 and 12 are only displaced in the Z direction.
Meanwhile, film 17 is paid off a supply reel(not shown), and when it reaches an illumination zone, it is fed by predetermined extent by predetermined extent feed rollers 18 which are driven by a stepping motor(not shown) or the like. At this time, film 17 is accurately positioned by pins 20 inserted through its perforations 17'. At this time, the restraint of film 17 by predetermined extent feed rollers 18 is released, and film 17 is exposed in a state held between and in close contact with film receiver 19 and pressing member 21. The film is thus exposed in a state between and in close contact with film receiver 19 and pressing member 21. For claiming the film between and in close contact with members 19 and 21, liner driver 14 is displaced in the Z direction(i.e., optical axis direction) by drive section 23 while it is in rattling-free engagement in guide 22, and pins 20 of film pressing member 21 are received with play in escapement grooves 19'.
After exposure, film 17 is further fed by predetermined extent feed to be taken up on a take-up reel(not shown).
With the prior art exposure apparatus as described above, the image projection system and film positioning system constitute respective independent units. Therefore, accurate setting of the two systems relative to each other requires complicated adjustments and takes a considerable time. Besides, very high accuracy of the positional relation can not be expected. Further, since the individual units are assemblies of many components, it is difficult to meet sufficient dimensional and geometrical accuracy inclusive of engagement accuracy. This means that it is difficult to obtain projection of the reticle pattern on the FPC film at accurate position thereof with reference to perforations of the film. In addition, optically partial out of focus in one side of the image and aberrations are liable. Therefore, it is difficult to obtain accurate pattern of exposure.